The thing i like about this lens is it has image stabilisation, but will it give me close shots of aircraft flying past at 400mph? Its either this or the un-stabilised 75-300mm USM, unless i can find a 70-300mm IS USM very cheap second hand. Just over a hundred is my max budget for this.

Airspeed has very little to do with how "close" a given focal length will get you. Although it does help to indicate that IS shouldn't be a priority. i.e. combined with the fact that you'll be shooting in daylight, you will probably also be using a fast enough shutter speed to make IS unnecessary.

What you do need to find out is how physically close you'll be to the aircraft, and while this may be obvious, don't forget to factor in altitude. Then use whatever Field of View Calculator you prefer to find out approximately how long a focal length you'd like to have. (FYI I just posted a link to a FoV Calculator I like in another thread.)

Or, since we've established that IS isn't a priority in this situation, just go with the 75-300mm since that's within your budget - Mark

I agree that framing is hugely important so getting a suitable focal length/range will be critical.

However, I wouldn't go so far as to say that IS isn't necessary as its necessity depends on the effect you're trying to get. If there are clouds in the background and you want to give an impression of speed by panning your shot so you get motion blur on the clouds in the background while the aircraft appears frozen in the foreground, you will need a relatively low shutter speed so IS may come in handy.

I have the 75-300 III non-USM version and most images coming out of it are completely useless. You are much better off using your 55-250 and crop down the image. If you had a bit more budget, I just recently upgraded to the Tamron SP 70-300 VC USD and it's absolutely incredible. That Tamron won EISSA and TIPA awards and is quite amazing. Canon's EF 70-300mm f/4-5.6 IS USM isn't far behind, but is a bit more expensive, so I would recommend the Tamron over it.

In all honesty, if you're looking for a 100$ telephoto lens, you're probably better off getting a 50mm f/1.8 and crop the image. The cheaper telephotos as the 75-300 III will just disappoint you.

And as was stated, with planes going that fast, you will be using a super high shutter speed (maybe 1/500 or 1/1000, maybe even more), so IS or non-IS won't really make a difference for this.